To be successful, HIV prevention programs require an understanding of the prevalence, nature, and context of risk practices in vulnerable communities. In Russia, the AIDS epidemic is concentrated among injection drug users (IDUs) and commercial sex workers (CSWs), but it appears to be spreading through their sex partners who serve as "bridges" into the general population. The goal of this study is to target and learn more about the "bridge population", and to monitor risk behavior in well-defined samples from both high risk groups and general population. To accomplish this, we propose to study individuals attending STI clinics in St Petersburg, Russia to identify if the clinics can be suitable sites for interventions aimed at curbing the spread of HIV among those who have sex with IDUs or CSWs. Taking advantage of previous and ongoing collaborations between researchers in St. Petersburg and Yale University School of Public Health, we propose a 2-year project with the following objectives: 1) To implement a procedure to conduct a cross-sectional behavioral survey in STD clinics in St Petersburg so they can be conducted on an on-going basis. 2) Use the behavioral survey to identify the proportion of STI patients belonging to "bridge populations". The results of this study will provide data needed to develop a program for prevention and control of STIs, including HIV, among populations at risk for acquiring HIV in St. Petersburg, Russia. These approaches are fundamental in developing responses to help control the largest current drug-user-focused HIV epidemic and reducing its impact, through sexual transmission, on the general population. The project we are proposing would be a first in Russia and could influence how the course of the Russian HIV epidemic unfolds and what responses are mounted. It is intended as a proof in principle that the currently existing STI clinic system can play a vital role in combating the HIV epidemic.